A conventional dynamoelectric machine comprises a housing and an elongate cylindrical stator within the housing having a plurality of stator slots carrying a stator winding. A rotor is received in a bore in said stator and is rotational relative thereto.
In order to increase efficiency, such dynamoelectric machines have employed liquid cooling of electrical components. The most effective method of cooling is to bring the liquid, such as oil, into direct contact with the heat producing parts. This is accomplished in a rotor by pumping the oil axially through the rotor windings so as to bring the oil into intimate contact with every part of every field winding conductor. A typical rotor is totally enclosed within a sleeve so as to contain this portion of the cooling within the field windings.
Stator, or armature, windings are typically cooled by spraying oil directly onto the end windings from jets in the rotor. This scheme does not provide direct cooling to the portion of the windings within the stator slots. The spray cooling method results in free oil in the generator interior, which results in power losses caused by the drag of the oil entrapped between the rotor and the stator. This system of cooling is effective only with a shorter core length. Alternatively, back iron cooling provided in the stator housing can be used. This form of cooling relies on conduction from the stator winding conductors to oil channels in the stator housing, through the stator slot insulation and the magnetic iron core, both of which have low thermal conductivity.
A preferred structure for cooling armature windings would apply the principal of the rotor field axial flow cooling, discussed above. Such structure would require the pumping of cooling oil from one end winding to the other through the stator slots. However, the armature windings are impregnated with a suitable varnish, or epoxy resin, to secure the windings against vibration, which might be caused by the alternating electromagnetic forces resulting from the alternating currents within the windings. Such vibration must be suppressed to prevent chafing wear of the winding conductor insulation. This problem does not occur with the field winding which carries direct current rather than alternating current.
The present invention is directed to overcoming one or more of the problems as set forth above.